getValidAdjacentLocations

Gets the valid locations adjacent to a given location in all eight
compass directions (north, northeast, east, southeast, south, southwest,
west, and northwest).
Precondition: loc is valid in this grid

getEmptyAdjacentLocations

Gets the valid empty locations adjacent to a given location in all eight
compass directions (north, northeast, east, southeast, south, southwest,
west, and northwest).
Precondition: loc is valid in this grid

getOccupiedAdjacentLocations

Gets the valid occupied locations adjacent to a given location in all
eight compass directions (north, northeast, east, southeast, south,
southwest, west, and northwest).
Precondition: loc is valid in this grid